#include <cstdio>
#include <cstring>
#include <ctype.h>
using namespace std;
int n,m,i,j;
char c[100001];
int beginx;
char permision[]="+-[]BDIPSX";
bool force_exit;
bool allert;
bool last_letter,not_X_P,not_S_D,rmd,L_appear;
char remind;
void refresh()
{
    allert=false;
    last_letter=false;
    not_X_P=false;
    not_S_D=false;
    L_appear=false;

}
bool notappear(char ch)
{
    int i,m;
    if(isalpha(ch)==true) return true;
    if(isdigit(ch)==true) return true;
    m=strlen(permision)-1;
    for(i=0;i<=m;i++)
    {
        if(ch==permision[i])
            return true;
    }
    return false;
}
bool valid(char ch)
{
    if(notappear(ch)==false)
        return false;
    if(ch=='+'||ch=='-')
    {
         allert=true;
         if(last_letter==false)
            return false;
    }
    if(ch=='[')
    {
          beginx++;
          last_letter=false;
    }
    if(ch==']')
    {
        beginx--;
        last_letter=true;
    }
    if(isalpha(ch)==true&&isalpha(remind)==true)
    {
        if(remind=='B'||remind=='b')
        {
            if(not_X_P==true) return false;
            if(ch!='X'&&ch!='x'&&ch!='P'&&ch!='p') return false;
            not_X_P=true;
            last_letter=true;
            allert=false;

        }
        else
        {
            if(ch=='I'||ch=='i')
            {
                if(not_S_D==true) return false;
                if(remind!='S'&&remind!='s'&&remind!='D'&&remind!='d') return false;
                not_S_D=true;
                last_letter=true;
                allert=false;
            }
        }
    }
    if(isdigit(ch)==true) allert=false;
    if(ch>='a'&&ch<='z')
    {
        if(L_appear==true) return false;
        L_appear==true;
        allert=false;
    }
    remind=ch;
    return true;
}
int main()
{
    //freopen("date.in","r",stdin);
    //freopen("date.out","w",stdout);
    gets(c);
    n=strlen(c)-1;
    while(n>=0)
    {
        refresh();
        force_exit=false;
        for(i=0;i<=n;i++)
        {
            if(valid(c[i])==false)
            {
                printf("ERROR\n");
                 force_exit=true;
                  break;
            }
        }
        if(beginx&&force_exit==false){ printf("ERROR\n"); force_exit=true;}
        if(allert==true&&force_exit==false){ printf("ERROR\n"); force_exit=true;}
        if(force_exit==false)
            printf("OK\n");
        gets(c);
        n=strlen(c)-1;
    }
    return 0;
}